A fuel cap to be used in the automobile or the like has to provide a god seal when it is completely secured, although it is just a simple part. The fuel cap is also required to enhance the operability from the early stage of the securing operation where the turning operation is started to the end stage of the securing operation where the turning operation is completed, for example, to reduce the turning amount of the opening/closing operation.
The conventional fuel caps describing those purposes are exemplified by Japanese Patent No. 2712115, JP-A-06-040262 or JP-A-2001-341537.
Japanese Patent No. 2712115 has proposed a cap, which is constructed to include a core corresponding to the closure body of the invention, and a sleeve. In this cap of Japanese Patent No. 2712115, the sleeve is made movable relative to the core and supports a seal ring. As a result, the cap is provided with closing means for closing the opening of a liquid filling port, and grasping means for grasping the liquid filling port to compress the seal ring between the sleeve and the liquid filling port.
JP-A-06-040262 has proposed a closure for a filler pipe of a tank. This closure comprises: a gasket to engage with a flange at one end portion of a filler pipe; a cap stem having a central portion made to extend into the filler pipe; a clamp ring for carrying a pair of clamp lugs adapted to engage with lower part of the flange formed at one end portion of the filler pipe; springs for pushing the clamp lugs to be engaged with the flange; a cam for keeping the clamp lugs out of engagement with the flange; and connection means for connecting the stem to the clamp ring so that the stem and the clamp ring may simultaneously move in angular directions.
JP-A-2001-341537 has proposed a fuel filling device for a fuel tank, which comprises: a casing body removably mounted on a fuel filling pipe; an operation unit for operating to open/close a fuel passage; seal means interposed between the casing body and a face of the fuel filling pipe; a spring arranged to bias the seal means towards the face; and cam means converting rotation of the device into a sealing force by which the seal means pushes the sheet face.
For example, Japanese Patent No. 2712115 has adopted a structure, in which the opening/closing operation of the fuel cap is completed by a turning operation of 45 degrees. However, it is difficult to obtain a space capable of pressing the seal ring tightly with only an amount of downward sliding by fastening of such a cap. Therefore, the fuel cap described in Japanese Patent No. 2712115 has a structure, in which the seal ring is pressed to the opening edge of the filler neck by a spring. Similarly, the fuel caps described in JP-A-06-040262 and JP-A-2001-341537 adopt the similar structure.
In this structure, in order to obtain a space to press the seal ring tightly, these conventional fuel caps also adopt the construction in which the spring elastically supports a sleeve for pressing the seal ring tightly. With only this construction, however, the seal ring pressed tightly may be fluctuated as a result of a load from the outside of the fuel cap or by the pressure of fuel vapor coming from the inside of the filler neck, thereby to deteriorate the sealing property. In case the fuel cap being inclined is fitted to the filler neck, moreover, it causes deterioration of the sealing property by which the pressure of the seal ring easily becomes insufficient where the spring may be further compressed. This is because the conventional fuel cap has been designed based upon the assumption that the cap is in a normal position.